Don't trust every study you hear. In an article
Conclusion: Don't let shoddy research methods give science a bad name.
- Regression to the mean: As the number of data points increases, we expect the average values to regress to the true mean…and since often the initial work is done on the basis of promising early results, we expect more data to even out a fortuitously significant early outcome.
- The file drawer effect: Results that are not significant are hard to publish, and end up stashed away in a cabinet. However, as a result becomes established, contrary results become more interesting and publishable.
- Investigator bias: It’s difficult to maintain scientific dispassion. We’d all love to see our hypotheses validated, so we tend to consciously or unconsciously select results that favor our views.
- Commercial bias: Drug companies want to make money. They can make money off a placebo if there is some statistical support for it; there is certainly a bias towards exploiting statistical outliers for profit.
- Population variance: Success in a well-defined subset of the population may lead to a bit of creep: if the drug helps this group with well-defined symptoms, maybe we should try it on this other group with marginal symptoms. And it doesn’t… but those numbers will still be used in estimating its overall efficacy.
- Simple chance: This is a hard one to get across to people, I’ve found. But if something is significant at the p=0.05 level, that still means that 1 in 20 experiments with a completely useless drug will still exhibit a significant effect.
- Statistical fishing: I hate this one, and I see it all the time. The planned experiment revealed no significant results, so the data is pored over and any significant correlation is seized upon and published as if it was intended. See previous explanation. If the data set is complex enough, you’ll always find a correlation somewhere, purely by chance.
By the way, I'm saddened to learn that psychology studies are rife with potential error given the small, homogeneous samples (n=20). So, dear reader, be skeptical when you read about so-called scientific findings, even ones I post here, and keep these points in mind.